The acidification of wells is the process for restoring permeability of subterranean formations by treating the formations with an acid, usually hydrochloric. Problems associated with acidification usually include corrosion of the well equipment and reactivity of the acid with the material immediately surrounding the well bore hole. To overcome these problems it is known to the art to use halogenated hydrocarbons as in situ sources of hydrochloric acid. For example U.S. Pat. No. 3,215,199 discloses the use of organic halides together with an alcohol and water which will provide HCl as a decomposition product in the formation. The advantage is that such decomposition occurs only slowly or not at all at ambient temperatures, but when such a treating composition reaches the temperatures present in the formation, decomposition occurs. The halogenated hydrocarbons taught in the '199 patent are the alkyl chlorides, bromides and iodides, such as the propyl chlorides, t-butyl chloride, allyl chloride, t-butyl iodide, epichlorohydrin, dihydroxychloropropane and the like. The alcohols taught therein are methyl, ethyl, isopropyl, butyl and the higher homologous alcohols as well as unsaturated alcohols such as allyl alcohol.
Another method of increasing the flow of fluids through a formation is disclosed in U.S. Pat. No. 3,288,216 wherein 1,1,1-trichloroethane is introduced into the well formation followed by an aromatic hydrocarbon solvent, eg toluene, and thereafter by an alcohol, preferably methanol. Such treatment is said to remove flow restricting materials from the formation.
A variation on the method of the '199 patent is disclosed in U.S. Pat. No. 3,297,090 wherein in aliphatic monochloride, together with an aqueous solution of an aliphatic alcohol and a catalyst containing cuprous ion, e.g. cuprous chloride, is injected to produce hydrochloric acid in the formation. U.S. Pat. No. 3,307,630 teaches the use of a reducing agent in addition to the cuprous ion to maintain it in that condition, i.e. the reducing agent converts any cupric ions produced back to the cuprous form.
In a more recent patent, U.S. Pat. No. 4,148,360, a method of acidizing employing C.sub.1 and C.sub.2 polyhalogenated aliphatic compounds, such as carbon tetrachloride, chloroform, tetrachloroethane, pentachloroethane, bromotrichloroethane, tetrabromoethane, dibromotrifluoroethane and the like polyhalo compounds. Water is also separately introduced into the formation to aid in the decomposition of the halogen hydrocarbon. The well is then "shut in" for a period of time sufficient to allow the acid to form and acidize the formation. This process is said to be useful in wells wherein the temperatures are in the range of 250.degree. to 700.degree. F. (or about 120.degree. to 370.degree. C.). U.S. Pat. No. 4,203,492 employs an aqueous solution of an alkali metal or ammonium fluoride salt and a liquid acid precursor, e.g. a halogenated C.sub.1 or C.sub.2 hydrocarbon, to produce a hydrohalic acid, which, in combination with the fluoride salt attacks the formation.
The present invention is an improvement which allows the treatment (acidizing) to take place more rapidly and at lower temperatures, thus allowing treatment of shallower wells.
The invention also provides for more complete reaction, thus preventing the release of chlorocarbon into the information as a potential contaminant of ground water.